Wavelength Division Multiplexing (WDM) is used to transmit a plurality of optical channels via an optical waveguide medium where each channel carries information signals within a network or system. Each channel within the WDM signal is associated with a particular wavelength, thereby increasing the information capacity of fiber optic systems. Such optical systems include, for example, local area networks (LANs), telecommunication systems and cable television systems. Depending on the optical system configuration and the transmission path, various optical and/or electrical amplifiers are required to provide the necessary optical power to efficiently transmit and amplify the WDM signal to each component within the network.
WDM optical networks have traditionally been used for long haul point to point networks. However, with the increasing demands on communication systems, WDM optical networks can also be used in smaller system configurations, such as local telephone or data networks. In these systems, communication signals are usually transmitted over a limited geographic area to various nodes within a network. A particular node can be configured to drop one or more information bearing or payload channels from the WDM signal, process the information contained in the dropped channels and add the channels containing new information to the WDM signal for transmission to other nodes in the network. An optical multiplexer present at each node may be used to drop the particular channel from the WDM signal and subsequently add the channel back to the WDM signal prior to transmission to another network node.
Because the transmission distance between nodes in these types of networks is relatively small, optical amplifiers are avoided in order to reduce the cost of the network. However, each optical component introduces optical power loss, measured in dBs. For example, the use of a fused fiber optical coupler may contribute a 3 dB loss to the transmission signal. This loss can accumulate among the various network components, but cannot exceed a predetermined power loss budget associated with the network configuration.
A service channel, usually outside the information bearing or payload channel bandwidth, is preferably included in these optical systems for carrying system housekeeping information, for example network monitoring and control signals as well as telemetry information, to and/or from nodes in the network. Because the service channel wavelength is outside the payload channel bandwidth, separate components configured to receive and process the service channel are required. These service channel specific components increase the power loss within the network unrelated to the payload channels where the extra loss is seen by the through channels passing to other network nodes. Moreover, these service channel components negatively impact the loss budget associated with the network.
Thus, there is a need to reduce the power loss associated with optical networks by combining the use of service channel components with payload channel components within an optical WDM network. There is also a need to provide these components at reduced expense.